GB2141226A - Optical measurement of human feet - Google Patents

Abstract

Apparatus for measuring the dimensions of a foot for shoe fitting purposes comprises a trough into which the foot is placed with arrays of light-emitters and receptors in the side-walls. The length of the foot is derived from determining where the toe and heel obstruct light beams across the trough between the arrays. A time-division multiplex system is used to give effective collimation of the light beams and so allow close packing of the emitters and receptors without interference between adjacent members of the arrays. Width and height of the foot are also measured. <IMAGE>

Description

SPECIFICATION Method and apparatus for the measurement of human feet The invention relates to a method and apparatus for the measurement of feet, principally to determine shoe size. Particularly for children, it is important to measure feet accurately when shoes are purchased.

Conventional methods of foot measurement require the foot to be placed in a measuring device which makes physical contact with the toe and heel and sides of the foot. This can lead to inaccuracies not only because of the limitations of the measuring device and its method of use but also because the child may involuntarily tense the foot during measurement.

For the above reason it is desirable to be able to measure the foot in a way which allows the foot to be free and without making contact with it with feelers or the like. Optical methods suggest themselves, where, for example, the length of the foot may be determined by the positions at which the toe and heel break a light beam projected across the foot. However, with such a system accuracy is difficult to achieve because the foot is remote from both the optical transmitters and the optical receptors and thus imposes constrictions on the required optical directivity of the equipment, and it is not possible to meet these economically by mechanical means. The present invention seeks to overcome this difficulty.

According to one aspect of the invention there is provided a method of measuring the length of a foot consisting in placing the foot between an array of light-emitters on one side and a corresponding array of light-receptors on the other side, each lightemitter being paired with a light-receptor; energising members of the light-emitter array; sampling the outputs of members of the light-receptor array, the energisation and sampling being effected in timedivision multiplex manner to activate only one emitter-receptor pair at a time; and deriving outputs representative of the positions of the response transitions caused by light-obstruction by the toe and the heel.

The use of time-division multiplex techniques in this way allows the response of each receptor to its corresponding emitter to be isolated from its response to other, adjacent, emitters. A kind of electronic collimation is thereby achieved, giving a precise correspondence between corresponding emitters and receptors. This allows close packing of the members of the arrays since the effects of optical spread are eliminated.

Time-division multiplex systems are conventionally used to allow a common processing channel to be shared by a number of input devices. This advantage acdrues also in the present invention, since the multiplexed receptors may feed a common output amplifier channel.

According to another aspect of the invention there is provided apparatus for measuring the length of a foot comprising a trough in which the foot is placed, the trough having side-walls, one of which carries an array of light-emitters and the other of which carries a corresponding array of light-receptors, each lightemitter being paired with a light-receptor; timedivision multiplexers for energising members of the light-emitter array and sampling the outputs of members of the light-receptor array so as to activate only one emitter-receptor pair at a time; and means for deriving outputs representative of the positions of the response transitions caused by lightobstruction by the toe and the heel.

Preferably each array extends along the whole of the respective side wall except for a region in the middle which will be obscured by even the smallest foot. This arrangement effectively sub-divides the arrays into toe and heel regions, and the whole of each array is scanned in the same time-division multiplex system. However, an alternative is envisaged where the heel and toe regions may be treated as separate arrays subject to their own multiplex systems.

In addition to length, the foot must be measured for width. It is possible to apply the same principles for width measurement as for length measurement, by arranging arrays of light-emitters and receptors across the trough at the toe and heel ends and by multiplexing to achieve electronic collimation in the direction of the length of the foot. However, the trough would then require an upstanding side behind the foot, with the consequence that the user must place his foot in a box-like trough. This is not convenient, and a better method is available. Since the base of the foot is in close contact with the floor of the trough, accurate width measurement can be achieved by means of an array of light-receptors in the floor of the trough which is shadowed by the foot.

Preferably, therefore, the floor of the trough has two further arrays of light-receptors, one near each side of the foot, means are provided for illuminating the foot from above, and means are provided for examining the outputs of the receptors to determine the width of the foot as given by its shadow on the light-receptors. Preferably the arrays at the two sides of the foot are illuminated by respective lamps which are energised alternately in conjunction with a multiplex system which samples the width receptor outputs.

It is necessary to measure the width of the foot at the widest part, and since in the interests of economy the width-receptor arrays should not be large it is hecessary to position the foot with the widest part over the arrays. The distance of the widest part of the foot from the toe or the heel is a proportion of the length of the foot. Placing the toe or heel against a reference mark is therefore not an adequate way to determine the position of the widest part. However, information is available from the length-receptor arrays of (a) the length of the foot and therefore the distance from the toe of the widest part and (b) the position of the toe. Therefore preferably there is provided a display for directing the user to move his foot to the appropriate position, taking account of the length measurement information.

While the display may be an arrangement of light-emitting or liquid-crystal diodes a preferred arrangement comprises a cathode-ray tube V.D.U.

This is particularly suitable when, as is preferred, the measuring apparatus is under the control of a programmed micro-processor. Thus, while it is possible to effect measurement by controlling the multiplexers with counter circuits and producing displays and outputs on a digital display unit, much greater flexibility is possible with the use of a micro-processor. For example, the manner of scanning the emitter-receptor arrays can be cyclic and sequential. When control is effected by circuitry employing counters and the like, the sampling procedure is fixed. However, if a micro-processor is employed, the scanning sequence can be changed according to circumstances.Thus, the initial scan may be sequential in a fixed order but when this has given an indication of the position of the toe and the heel then the scanning pattern can be altered to scan only those emitter-receptor pairs in the region of the toe and the heel, so that an accurate measurement can be derived rapidly.

A particularly useful feature of a micro-processor is that it allows the use of soft-ware which may employ a statistical approach to measurement which enhances accuracy available from emitter-receptor arrays of a given spacing pitch. Bytaking a number of readings of length and/or width with the foot in different positions it is possible to analyse the outputs statistically to give a resolution accuracy which may be an order of magnitude better than the spacing pitch of the emitter-receptors. In this way the number of emitters and receptors may be reduced.

The micro-processor can be used to generate a display which encourages the suer to move his foot so that the statistical measurement technique described above can be employed. For example, if the user is required to move his foot until an indicator representing his foot position reaches a datum line on the screen, the datum line can be moved to require the foot to be moved.

The measurement of length and width have been discussed. A preferred additional measurement is the height of the foot at a given position. This gives an indication of how arched the foot is. For height measurement it is preferred to provide an extra set of emitter and receptor arrays in the sidewalls of the trough. These extra arrays may be multiplexed in the same way, and indeed in the same system, as the length arrays. The foot will be positioned as described above for width measurement and the part of the height array which is examined will depend on its distance from the toe, having regard to a table of values programmed into the micro-processor.

The foregoing description has been made with reference to the measurement of one foot and a measuring device having one trough, the feet being measured one at a time. As an alternative the apparatus may be provided with a trough for each foot.

The invention will be further described with reference to the accompanying drawings, ofwhich:- Figure lisa perspective view of foot measuring apparatus in accordance with the invention; Figure 2 is a diagram showing the arrangement of the length receptor arrays of the apparatus of Figure 1; Figure 3 is block circuit diagram of the length measuring part ofthe apparatus of Figure 1; Figure 4 is a diagram illustrating the width measuring features of the apparatus of Figure 1; Figure 5 is a block circuit diagram showing the multiplex arrangement for the width detectors of Figure 4; and Figure 6 is a circuit diagram of the output circuit for processing the receptor signals.

Referring to Figure 1 there is shown the apparatus which has a base tray 1 of moulded plastics material on which is mounted by way of struts 2, a display console 3. The tray has a trough 4 in which a user may place his feet one at a time, while facing the console 3. The console has a cathode-ray tube display 5 and a light-pen 6. To use the apparatus, the user touches the screen with the light-pen, whereupon a horizontal datum line will be displayed with an arrow indicating the position of the foot with respect to the datum line. The user moves his foot in the direction indicated until the arrow reaches the datum line the screen is touched with the light-pen when a display will be given of the shoe fitting or fittings recommended, on the basis of length and width measurements taken in the manner two be described.

In the left-hand side wall of the trough there is an array oflight-emitting diodes. The array may be regarded as being in three parts. Firstly, there is an essentially linear part 7 which is the heel part of the length array. Secondly, there is another essentially linear part 8 which is the toe part of the length array.

Thirdly, there is a rectangular part 9 which is the height array. These arrays have corresponding arrays of light-receptors in the right-hand side walls of the trough. Also, in the floor of the trough there are arrays of width light-receptors, shown at 10.

These respond to the light from lamps 11 at the underside ofthe console, in a manner to be described with reference to Figure 4.

Referring now to Figure 2 there is shown the form of one of the length receptor arrays. The light receptors are light-responsive diodes and in the arrays they correspond one-for-one with the lightemitting diodes of the emitter arrays. The receptors of the heel part of the length array are shown at 7a.

This part of the array is a line inclined upwardly and rearwardly since it should correspond with the most rearward part of the heel, which rises with foot size.

Similarly, the toe part of the length array has receptors 8a in a line which rises forwardly. The gap between the front of the heel array and the back of the toe array represents a length smaller than the smallest foot measurable on the apparatus.

Because of the physical sixe of the discrete emitter and receptor diodes it is not possible to space them closerthan about 0.1", and this would determine the resolution of the length measurement. In order to overcome this limitation the array comprises two staggered lines of diodes, the effective spacing being thus reduced to 0.05". Such close packing is made possible by the multiplexing technique to be described. The final part of the receptor array in the right-hand side wall of the trough is a rectangular array 9a of height-receptor diodes corresponding to the emitter array 8.

Referring now to Figure 3 there is shown the block circuit diagram for the length measuring arrays 7, 7a, 8, 8a and 9, 9a. It should be explained that although arrays 9, 9a are for height measurement, they are included in the multiplexing system of the length arrays for convenience. The apparatus is under the control of a micro processor 13 which comprises a central processing unit 15, a read-only memory 16 and a random-access memory 17. The display unit 5 of Figure 1 is driven by the CPU 15.

Basically, the emitters 7, 8, 9 are divided into sixteen groups of sixteen, allowing for a maximum number of 256. The groups are shown at 18a, 18b etc. Similarly, the receptors are divided into sixteen groups 19a, 19b etc. The emitters are driven by a set of sixteen driver stages 20 (only two of which are shown). The driver stages are activated in sequence by the stepping output of a sixteen way multiplex unit 21.

The sixteen groups of emitters are connected respectively to different enabling outputs of another sixteen way multiplex unit 22. This multiplex unit has an additional gating input via a transistor 23 fed from the CPU. This accurately gates the output pulses from the emitters and avoids the effect of different build-up and decay characteristics of the emitters. The two multiplex units are driven by the CPU to address specific diodes sequentially one at a time.

The receptor groups 19a, 19b, have respective members of each group connected to the sixteen inputs of a multiplexing switch 24. The sixteen groups of receptors are connected respectively to be enabled by outputs on the sixteen lines of a group multiplex unit 25. The two multiplex units 24,25, are driven by the same outputs from the CPU as the units 21, 22. This ensures that the emitter receptor pairs of the arrays are activated one by one in sequence so that there is no risk of a signal being detected from a receptor in response to light from any emitter other than its pair. It is this feature which removes the mechanical and optical constrictions on alignment which would otherwise be required and which allows close packing of the emitters and receptors.

Output signals from the receptors are received when the light path between the receptor and the associated emitter is not obstructed. Otherwise no output pulses are received from the receptor. The output signals are passed through a common amplifier 26 to the CPU 15 which stores the data in the RAM for analysis.

The micro-processor can make many successive measurements and use statistical analysis of the results to improve accuracy. By reference to programmed tables the required position of the toe canbe determined for optimum width measurement and the cathode ray tube display can be driven accordingly to bring the foot into place. Should the foot obscure the diode at one extreme end or the other of the array, no output is given by the display since the foot is out of range and requires to be moved to initiate the display.

Referring now to Figure 4there is shown schematically the arrangement for the width measurement for the foot. The width arrays of receptors in the floor of the trough comprise an array 10a for the left-hand side and an array 1 Ob for the right-hand side. The two arrays are illuminated respectively by highpower LED emitters 11 a and 11 b. the two emitters are pulsed in turn and the receptor arrays are time-division multiplexed so that responses are detected through a common amplifier, the timing of the response being indicative of the particular receptor responsible. The foot having been positioned over the width receptors in the manner described, data representative of the width of the foot can be derived by reference to the receptors shadowed by the foot.

The pulsing of the various emitters of the apparatus not only identifies them in the time-division multiplex system but also allows electrical filtering of the signals to avoid the effects of ambient light on the receptor signals. Ambient light effects may also be reduced with the use of infra-red filters.

The VDU display can be used for promotional displays when the apparatus is not in use for measurement. Thus, computer-initiated advertising or other information may be displayed. Alternatively the screen may display signals from a video tape recorded.

Referring now to Figure 5 there is shown the block circuit diagram for the width-measuring arrangement of Figure 4. In this example each left-hand and right-hand array 10a, lob, has three rows of lightresponsive diodes. Electrically, the first row of array 10a is continuous with the first row of array lob, the second rows are continuous and the third rows are continuous, so that electrically there are three rows in all.

In Figure 5 the three rows of receptors are shown at 30,31 and 32. Each row is sub-divided into groups of sxiteen, the groups being numbered 33, 34 etc.

Sampling of the receptor outputs by the multiplexing arrangement is effected in a manner analogous to that described above with reference to Figure 3. A group multiplex enables the groups one at a time by applying a bias potential to the group. The outputs from the diodes in the three rows are sampled by a multiplex switch for each row, that for row 30 being shown at 35, and the other being designated 36, 37.

By appropriate contol of the multiplexing signals, the diodes are effectively sampled one at a time. The outputs from the multiplex switches 35, 36 and 37 are applied to a common amplifier 38, the output from which provides data for the micro-processor 13 (Figure 3) which controls the multiplexing. An important feature of the Figure 5 circuit, which may also be provided in the Figure 3 arrangement, is the provision of isolating diodes 39 in series with the light-responsive diodes shown at 40. The isolating diodes prevent cross-coupling between the lightresponsive diodes and thereby help prevent spurious responses caused by high levels of ambient light or simultaneous illumination of adjacent receptors by the emitter diodes.

Selected receptors at the extreme ends of the arrays may be identified so that if they are obscured it means that the foot lies over the end of the array. A display is then given requiring the user to move his foot in the appropriate direction.

Referring now to Figure 6 there is shown detail of the amplifier circuit for amplifier 26 of Figure 3 or amplifier 38 of Figure 5. The amplifier circuit includes an amplifier 41 which is a.c. coupled to the output from the multiplex switch 24 or 35 to 37 by a capacitor 42. A threshold detector 43 receives the output from amplifier 41 and also a settable threshold bias from a variable resistor 44. An output is given from the threshold detector if the input exceeds the threshold and this output is applied to an AND gate 45. The other input to the AND gate is derived from the scanning output clock of the micro-processor. The scanning output is a pulse which actuate the illuminating LED within each period of activation by the multiplexing arrangement. The timing of the multiplexing is controlled by a multiplexing clock which synchronisesthe microprocessor.The output signal from gate 45 is applied to a flip-flop circuit 46 which is triggered by the multiplex clock outout. The result is that an output data pulse to the micro-processor is given on line 47 if and only if a diode response is received which is above a certain threshold, is within the clock period of the light-emission from the LED's and is within the multiplex clock period.

The invention is not restricted to the details of the foregoing description made with reference to the accompanying drawings. For example, the lightresponsive diodes may be replaced by phototransistors. As a further alternative it is possible that the emitters and receptors be made as a large scale integrated circuit matrix, without discrete components. The outputs from the receptors have been described as occurring when the light path is not obscured. The converse may be true - an output being given when the light path is obscured and being supressed when the light path is not obscured.

Claims (12)

1. A method of measuring the length of a foot consisting in placing the foot between an array of light-emitters on one side and a corresponding array of light-receptors on the other sid, each light emitter being pair with a light-receptor; energising members of the light-emitter array; sampling the outputs of members of the light-receptor array, the energisation and sampling being effected in time-division multiplex manner to activate only one emitterreceptor pair at a time; and deriving outputs representative of the positions of the response transitions caused by light-obstruction by the toe and the heel.

2. Apparatus for measuring the length of a foot comprising a trough in which the foot is placed, the trough having side-walls, one of which carries an array of light-emitters and the other of which carries a corresponding array of light-receptors, each lightemitter being paired with a light-receptor; timedivision multiplexersforenergising members of the light-emitter array and sampling the outputs of members of the light-receptor array so as to activate only one emitter-receptor pair at a time; and means for deriving outputs representative of the positions of the response transitions caused by light obstruction by the toe and the heel.

3. Apparatus as claimed in claim 2 wherein each array extends along the whole of the respective side wall except for a region in the middle which will be obscured by even the smallest foot, thereby su bdividing the arrays into toe and heel regions.

4. Apparatus as claimed in claim 3 wherein the whole of each array is scanned in the same timedivision multiplex system.

5. Apparatus as claimed in any of claims 2 to 4 wherein the floor of the trough has two further arrays of light-receptors, one near each side of the foot, means are provided for illuminating the foot from above, and means are provided for examining the outputs of the receptors to determine the width of the foot as given by its shadow on the lightreceptors.

6. Apparatus as claimed in claim 5 wherein the arrays at the two sides of the foot are illuminated by respective lamps which are energised alternately in conjunction with a multiplex system which samples the width receptor outputs.

7. Appartus as claimed in claim 4 or claim 5 wherein a display is provided, the display being driven by outputs derived from the light-receptor arrays in the side-walls of the trough, the outputs being given in accordance with (a) the length of the foot and (b) the position of the toe and the display being arranged to give indications which direct the user to move his foot to a position where the widest part of the foot covers the arrays in the floor of the trough.

8. Apparatus as claimed in claim 7 wherein the display is a cathode-ray tube visual display unit (VDU) and the measuring apparatus is under the control of a programmed micro-processor which drives the display.

9. Apparatus as claimed in claim 8 wherein the micro-processor is programmed to employ a statistical approach to measurement, taking at least length measurements with the foot in a number of different longitudinal positions in the trough, and the display is effective to encourage the necessary movements of the foot.

10. Apparatus as claimed in any of claims 2 to 9 wherein an extra set of light emitter and receptor arrays is provided in the trough side-walls for the measurement of height of the foot.

11. Apparatus as claimed in claim 10 wherein the extra arrays are multiplexed in the same multiplexing system as the first-mentioned arrays in the trough side-walls.

12. Apparatus for foot measurement substantially as hereinbefore described with reference to Figures 1 to 6 or Figure 7 of the accompanying drawings.